The invention relates to rotary mechanisms, particularly to rotary compressors or expansion engines in which the rotor has a planetary motion within a housing and the peripheral surface of the rotor is substantially a hypotrochoid and the inner surface of the housing is substantially the outer envelope of the relative rotary motion of the rotor. Such a compressor or expansion engine is disclosed in U.S. Pat. No. 3,387,772 granted June 11, 1968 to Wutz and in British Pat. No. 583,035 granted on Dec. 5, 1946 to Maillard and is generally known as a Maillard-type compressor. The invention will herein be described in terms of compressor operation although as will be apparent it is also applicable to expansion engines.
Various trochoidal-type compressors have been proposed in the part in which either the outer periphery of the rotor or the inner periphery of the rotor housing is a trochoidal surface, either an epitrochoid or a hypotrochoid. For example, U.S. Pat. No. 3,671,153 granted on June 20, 1972 to Luck shows a compressor in which inner surface of the rotor housing is an epitrochoid. A rotary mechanism having the geometry of the rotor and rotor housing shown in the Luck patent is generally known as a Wankel-type rotary mechanism. It has been determined that a Maillard-type compressor has the advantage in that the minimum volume of each working chamber is reduced substantially to zero at the end of the discharge stroke of each working chamber thereby providing a compressor with high volumetric efficiency.
The efficiency of a rotary compressor depends on the provision of adequate sealing for each working chamber. In a Maillard-type compressor, it is essential to provide sealing between each rotor nose portion and the inner periphery of the rotor housing as well as between the point or points on the rotor housing periphery which generate or trace the hypotrochoid surface of the rotor as the rotor rotates relative to the housing. However, in the case of a Maillard-type compressor, each rotor nose or apex portion, instead of being pointed as in a Wankel-type configuration, is rounded and the seal contact line with the rotor housing shifts about the rounded nose portion as the rotor rotates relative to the rotor housing. Therefore, in the case of a Maillard-type compressor, a radially movable seal bar carried in a slot extending axially across the nose portion of the rotor would have to shift radially relative to the rotor to maintain seal contact with the rotor housing. Any such required radial motion of the rotor apex or nose seals necessarily reduces the effectiveness of the seal since because of friction forces and the short response time, the seal may not maintain seal contact with the rotor housing. Also, such required seal motion would increase the amount of lubrication required to minimize seal wear.